1. Field of the Invention
This invention relates to an elevator overspeed protection apparatus or in other words, an elevator governor, for operating an elevator for elevating people and/or loads with safety.
2. Description of the Prior Art
FIGS. 93(1) and 93(2) are a plan view (FIG. 93(1)) and a front elevational view (FIG. 93(2)), respectively, showing a conventional example of an elevator overspeed protection apparatus disclosed, for example, in Japanese Patent Laid-Open Application No. Heisei 5-147852. Referring to FIGS. 93(1) and 93(2), reference character 12 denotes a car of the elevator, 13 a base provided on the car 12, 14 an arm formed by a pair of parallel links, 15 a fulcrum provided on the base 13 for supporting the arm 14 for pivotal motion, 16 a pickup mounted for pivotal motion at an end of the arm 14 for detecting the speed of the car 12, 16a a pair of magnets provided in an opposing relationship to each other, 16b a yoke to which the magnets 16a are secured, 17 a balance weight mounted at the other end of the arm 14 so as to be balanced with the pickup 16, and 18 a conductor such as a guide rail provided fixedly alongside the car 12, and magnetic fluxes going out of the magnets 16a of the pickup 16 form a first magnetic circuit passing through a plate-formed portion extending from the center of the conductor 18 toward the car 12 and the yoke 16b. Meanwhile, reference character 19 denotes a elastic spring for providing a resisting force to a displacement of the balance weight 17 by pivotal motion of the arm 14. The arm 14, the fulcrum 15, the pickup 16, the balance weight 17 and the elastic spring 19 form a conversion apparatus which converts a force acting upon the magnets 16a by eddy currents generated in the conductor 18 when the car 12 runs into a displacement of the magnets 16a in the running direction of the car 12. Reference character 20 denotes a brake apparatus including a car stopping switch 20a which is actuated in response to a displacement or the balance weight 17 and an emergency stopping operation mechanism not shown.
Subsequently, operation will be described. The magnetic circuit formed by the magnets 16a and the yoke 16b makes a magnetic field perpendicular to the plane of a plate-formed portion of the conductor 18 present between the magnets 16a. When the car 12 moves upwardly or downwardly and the magnetic field moves in the plate-formed portion of the conductor 18, eddy currents to cancel a variation of the magnetic field are generated in the conductor 18, and in the pickup 16, a force (drag) in the direction opposite to the running direction of the car 12 which resists the movement of the car 12 is generated with a magnitude corresponding to the speed of the car 12. This force is converted into a displacement of the pickup 16 and the balance weight 17 in the upward or downward direction by the arm 14 and the elastic spring 19 as seen in FIG. 94.
Then, when the moving down speed of the car 12 becomes equal to a first over speed (normally equal to approximately 1.3 times a rated speed which is an ordinary running speed) higher than a predetermined value, the pickup 16 is acted upon by an upward force corresponding to the speed to displace the balance weight 17 downwardly. Then, in response to the displacement, the car stopping switch 20a provided for the brake apparatus 20 is rendered operative to intercept the power source for the elevator driving apparatus to stop the car 12. Even when the car 12 reaches a second over speed (normally equal to approximately 1.4 times of the rated speed) by some cause, the balance weight 17 is further displaced in response to the speed so that an emergency stopping apparatus (not shown) provided for the car 12 is rendered operative by the emergency stopping operation mechanism provided for the brake apparatus 20 to stop the car 12 immediately.
Since the conventional safety apparatus for an elevator is constructed in such a manner as described above, when the magnetic field moves in the conductor 18, eddy currents are generated so as to cancel a variation of the magnetic field in the conductor 18 and a force (drag) in the direction to resist the movement of the car 12 is generated in the pickup 16 with a magnitude corresponding to the speed of the car 12. However, the conventional safety apparatus for an elevator has a subject to be solved in that, generally, due to the physical property of eddy currents generated in a metal conductor, the relationship between the speed V and the force f generated by the pickup 16 is such that, as seen in FIG. 95, when the speed is low, the variation rate of the generated force f is high, and as the speed V increases, the variation rate of the generated force f decreases. In particular, the conventional safety apparatus for an elevator has a subject to be solved in that, as the speed of the car 12 increases to the rated speed V0 (the displacement of the balance weight 17 then is P0) which is an ordinary running speed, to the first over speed V1 (the displacement of the balance weight 17 then is P1) and then to the second over speed V2 (the displacement of the balance weight 17 then is P2), the difference between the generated forces f0, f1 and f2 decreases and, although the danger increases, the difference in force to actuate the brake apparatus 20 decreases and also the set position of an operation point of the brake apparatus 20 becomes difficult, resulting in increase in occurrence of a malfunction, increase in dispersion of the operation speed and decrease in safety.
Further, since the characteristic of the spring force F2 of the elastic spring 19 relative to the displacement Z of the pickup 16 normally is such a linear relationship as illustrated in FIG. 96, the characteristic of the displacement of the pickup 16 relative to the speed V of the car 12 exhibits a higher variation rate of the displacement within a range of movement of the car 12 in an ordinary operation condition as seen in FIG. 97. Consequently, since the arm 14 is always pivoted over a great extent in an ordinary operation of the car 12, the conventional safety apparatus for an elevator has a subject to be solved in that a malfunction of the brake apparatus 20 sometimes occurs and the life of the fulcrum 15 which is a supporting portion for the pivotal motion is reduced.
Further, in the conventional elevator speed controller, when the car 12 is swung in a horizontal direction by a one-sided load upon movement of the car 12 or when passengers enter the car 12, the distances of the gaps (air gap portions) through which magnetic fluxes of the pickup 16 path are varied and the generated force by the pickup 16 is varied, and consequently, the conventional elevator overspeed protection apparatus has a subject to be solved in that also the displacement of the balance weight 17 is varied and detection of the operating speed of the car 12 becomes unstable, by which a malfunction of the brake apparatus 20 is sometimes caused.
Furthermore, the conventional elevator overspeed protection apparatus has a subject to be solved also in that detection for improving vibrations when the car 12 moves or when passengers enter the car 12 cannot be performed.
Besides, the conventional elevator overspeed protection apparatus has a subject to be solved in that, since it is placed on the car 12 and is heavy with a great number of mechanical sections which require a large space, the driving efficiency thereof is low and it cannot be carried readily.
In addition, the conventional elevator overspeed protection apparatus has a subject to be solved in that, since only a running speed of the car 12 is detected, when the car 12 is brought out of a controllable range and advances into a top pit section although it is running at a speed which is not a dangerous speed, the danger cannot be detected and emergency stopping does not operate, which is dangerous.